I recently bought an 06 4 cyl 4X4 with 5 spd manual transmission. It has 51k miles on it and seems in good shape all around. I've noticed, however, a vibration at around 45-50mph-felt through the steering wheel mainly. It pulses at about 2 second intervals-1 sec of vibration, 1 sec quiet. It's a rapid, slight vibration, not at all like unbalanced wheels, and seems to disappear when I let off the gas. Also, I can't seem to feel it in 4th gear, only 5th. which makes me think it must be a transmission issue. Anybody have any ideas? (Wheels just balanced, by the way, with no effect.)

Thanks for the comments. I've checked air pressure and had wheels balanced with no effect. The vibration feels like it's in the drive train rather than something to do with wheels. Gonna change fluids in tranny, diff, and transfer case, though I don't expect that to cure it.

I need to check the manual again, but I think 40-45 might be below the power band for 5th gear. "Power band" is my interpretation but somewhere in the manual I read the recommended speed range for each gear...the 5th thing stuck in my mind, so now I don't shift into 5th until I'm up to speed above 50 to 55 mph. If you start doing that and don't notice the strange vibration any more...I wouldn't worry about it further.

Actually, if I don't shift until about 55mph then the vibration doesn't occur, so maybe it's got to do with the "power band," as you phrase it. I think I'll take your advice and quit worrying about it! Thanks.

In the interest of full disclosure: I checked the manual for my 2007 4cyl/5spd/4x4 Access Cab. What I had read was recommended shifting speeds. Generally speaking they recommend the shift from 4th to 5th at 45 mph (39mph at low altitude). Where I'm at in South Central Alaska, I noticed an acceleration lag (or lugging) when I shifted to 5th below 50 mph or tried to maintain a speed below 50 mph. My old brain must have developed the "power band" theory. The older I get the more I believe in the KISS (Keep It Simple Stupid) principle.

I can agree with what your saying...but he started the thread referencing MPH, so I kept it there. Plus the manual references recommended shift speeds, not RPM. But now you've got me thinking...so I'll be looking at what my ranges translate to in RPM. Besides a reference point is a reference point...whichever way you translate it.